Method and arrangement in a telecommunications system

ABSTRACT

A receiving unit or a transmitting unit of a wireless network, for facilitating noise and interference measurements on an air interface. The receiving unit includes: a network interface which obtains information relating to a time-varying layout of a silent resource element (RE) grid; an electronic memory having code in communication with the network interface which stores the information; and a processing unit in communication with the electronic memory that takes a presence of a silent RE grid into account in the reception of a control or a data channel. 
     A method for a receiving/transmitting unit of a wireless network for facilitating noise and interference measurements on an air interface is described. Information relating to a time-varying layout of a silent resource element (RE) grid is obtained and a presence of a silent RE grid is taken into account in the reception of a control or a data channel.

TECHNICAL FIELD

The present invention relates to a method and arrangement in atelecommunications system. (As used herein, references to the “presentinvention” or “invention” relate to exemplary embodiments and notnecessarily to every embodiment encompassed by the appended claims.)More specifically, the present invention relates to facilitatingInter-cell interference measurement.

BACKGROUND

This section is intended to introduce the reader to various aspects ofthe art that may be related to various aspects of the present invention.The following discussion is intended to provide information tofacilitate a better understanding of the present invention. Accordingly,it should be understood that statements in the following discussion areto be read in this light, and not as admissions of prior art.

The invention is described with some references to LTE, but it should benoted that it conceivably can be applied to other systems as well,including e.g. WCDMA. It should also be noted that the invention isequally applicable both in the downlink as well as the uplink of awireless system.

Signal and channel quality estimation is a fundamental part of a modernwireless system. The nose and interference is used not only in thedemodulator, but is also an important quantity when estimating, forexample, the channel quality indicator (CQI). The following is notedwith LTE in mind, but the principles are valid for most wirelesssystems.

The interference can be estimated from the common reference symbols (RS)that are present in the time—frequency grid of an OFDM based system(e.g., LTE). An element in the time—frequency grid is referred to as aresource element (RE). The received signal in a RE can be written asr=Hs+n, where H is the channel response and s represents the transmittedsymbols. The term, n, is the (unknown) noise and interference. The noiseand interference show different characteristics in resource elements(RE) that hold RS, data, and control signaling; we therefore denote thereceived noise/interference for the different signaling types by I_RS,I_d, and I_control, respectively.

It is noted that the interference term in a RE containing RS, I_RS, at aspecific user equipment (UE) can be estimated by the UE since s areknown symbols and H is given by the channel estimator. It is furthernoted that the interference on REs with data (that is scheduled for theUE in question), I_d, also can be measured as soon as the (data)symbols, s, are detected (at this moment they can be regarded as knownsymbols). Similarly, to estimate I_control, the control symbols mustfirst be detected.

BRIEF SUMMARY OF THE INVENTION

The statistical characteristics of the (inter-cell) interference may besignificantly different, depending on whether the interferenceoriginates from

1. reference symbols from neighbouring cells

2. data signalling from neighbouring cells

3. control signalling from neighbouring cells

Each of these three categories can have different transmission power andspatial characteristics.

For accurate data channel COQI computation the UE must have goodstatistics of the interference that hits the data channel (which is amixture of the three categories mentioned above), I_d. Ultimately, thisinterference statistics should be measured on the data channel itself;however, this measurement is limited to resource entities (i.e.,time-frequency slots) that contain data scheduled to the particularuser. The limited number of interference samples can significantlypenalize the accuracy of the statistics estimate. Moreover, inmultiuser-MIMO (i.e., spatial division multiple access) systems, severalusers may be assigned the same data REs, which in effect prohibits theUE to separate the inter-cell interference from the intra-cellinterference, if the measurement is performed on data REs.

Alternatively, the interference measurement can be performed on REscontaining a RS. However, the statistics of the interference that hitsthe RS, may have significantly different statistics than theinterference on the data channel (or the control channel). There is alimited set of RS, and in particular for MIMO, where the positionholding a RS on one antenna is empty for a neighboring antenna,therefore the interference hitting a RS will to a larger extent comefrom RSs of the neighboring cells. In particular in lightly loadedsystems, I_RS, may be significantly different (typically substantiallylarger) than I_d, because possibly data is not allocated to all resourceblocks (RB) in the neighboring cells. The statistics of the measuredinterference term may therefore deviate significantly from theinterference that hits the data channel. The RS grid for a RB in case of1, 2 and 4 Tx antennas is illustrated in FIG. 1. Between cells, the RSis shifted in frequency domain.

For two Tx antennas only three frequency shifts for common RS exists.This will lead to that not all data interference can be measured.Furthermore, the first three OFDM symbols might see control channelinterference instead of data interference. Since control signaling maybe differently power controlled than the data, the interference estimateobtained on these RS may not reflect the interference present when datais transmitted. If common RS in the later part of sub-frame is removed(for example because dedicated RS are inserted instead) it might benecessary to measure interference on data REs.

According to one aspect of the present invention a cell specifictime-varying grid of data REs (referred to as the silent RE grid in thefollowing) is introduced, for which no data is allocated; that is, thetransmitter will be silent on this grid. The grid is known to both thereceiving and the transmitting unit.

According to a further aspect of one embodiment of the present inventionthe receiving unit are able to measure the statistics of the signal thatis received on the silent RE grid; this signal, originates completelyfrom inter-cell signals that interfere with the data channel.

The measured inter-cell interference can, for example, be used as abasis for channel quality (CQI) reporting and/or for interferencesuppression purposes in the receiving unit.

One advantage according to an aspect of an embodiment of the presentinvention is that a statistics measurement, performed on the silent REgrid, is computationally trivial, because no data must be decoded toobtain the residual noise and interference.

According to a further aspect of another embodiment of the presentinvention, the silent RE grid, could be randomized in consecutive (infrequency and time) resource blocks, to minimize the effects ofpotentially overlapping grids of neighbouring cells.

According to a further aspect of another embodiment of the presentinvention, the layout of the cell specific silent RE grid can be derivedwith little, or no, signalling overhead; it could for example be derivedfrom the cell ID and other information that is known to both thereceiving and the transmitting unit.

According to a further aspect of another embodiment of the presentinvention, a similar approach can be used to estimate the interferencethat hit the control channel, I_controls by introducing another silentRE grid on the control channel (e.g., potentially up to the first threeODFM symbols in an LTIE subframe).

According to one aspect of the present invention a method in a method ina receiving unit of a wireless network, for facilitating noise andinterference measurements on an air interface is provided. The methodcomprises the steps of obtaining information relating to a layout of asilent RE grid, and taking the presence of a silent RE grid into accountin the reception of a control or a data channel.

According to another embodiment of the present invention, the step ofobtaining information comprises using a pseudo-random sequence togenerate said layout of said silent RE grid, and synchronising saidpseudo-random sequency in each frame by deriving a seed for saidpseudo-random sequency from a Cell ID and a Frame Index.

According to another embodiment of the present invention the step ofobtaining information comprises receiving said layout of said silent REgrid through signalling.

According to another embodiment of the present invention the methodincludes the step of collecting statistics relating to the inter-cellinterference based on measurements on said silent RE grid, and usingsaid statistics to estimate any or all of a channel quality indicator,the inter-cell interference power that hits the channel, the co-variancematrix of the inter-cell interference that hits the channel, the fullprobability distribution of the inter-cell interference.

Further characteristics of the invention and advantages thereof will beevident from the following detailed description of embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description of embodiments of the present invention givenherein below and the accompanying figures, which are given by way ofillustration only, and thus are not limitative of the present invention.

FIG. 1 is an RS grid for a RB in case of 1, 2 and 4 Tx antennas;

FIG. 2 is a block diagram of a receiver unit of the present invention.

FIG. 3 is a block diagram of a transmitting unit of the presentinvention,

DETAILED DESCRIPTION

Referring now to the drawings wherein like reference numerals refer tosimilar or identical parts throughout the several views, and morespecifically to FIG. 2 thereof, there is shown a receiving unit 100, ora transmitting unit 110, as shown in FIG. 3, of a wireless network, forfacilitating noise and interference measurements on an air interface.The receiving unit 100 comprises a network interface 12 which obtainsinformation relating to a time-varying layout of a silent resourceelement (RE) grid. The receiving unit 100 comprises an electronic memory16 having code in communication with the network interface 12 whichstores the information. The receiving unit 100 comprises a processingunit 14 in communication with the electronic memory 16 that takes apresence of a silent RE grid into account in the reception of a controlor a data channel. In the transmitting unit 110, the processing unit 14takes the presence of a silent RE grid into account in the transmissionof a control or a data channel

The processing unit 14 can use a pseudo-random sequence to generate thelayout of the silent RE grid, and synchronizing the pseudo-randomsequence by deriving a seed for the pseudo-random sequence fromparameters. The pseudo-random sequence can be synchronized in each frameby the processing unit 14 based on the parameters that includes a cellID and a frame index. The layout of the silent RE grid can be receivedthrough signaling by the network interface 12.

The electronic memory 16 can collect statistics relating to inter-cellinterference based on measurements on the silent RE grid. The processingunit 14 can use the statistics with the code to estimate any or all of;a channel quality indicator, inter-cell power that hits a channel, aco-variance matrix of the inter-cell interference that hits the channel,a full probability distribution of the Inter-cell interference; and sendthe signal through the network interface 12. The processing unit 14 canrandomize the silent RE grid in consecutive, in frequency and time,resource blocks (RBs). The processing unit 14 can derive the silent REgrid with essentially no signaling overhead.

The processing unit 14 can of introduce another silent RE grid on acontrol channel to estimate the interference that hits the controlchannel using the code in the electronic memory 16. The processing unit14 can coordinate each silent grid of neighboring cells in the wirelesssystem such that there is no significant overlap. For each subframe, theprocessing unit 14 can group resource blocks into resource windows whereeach resource window is a group of contiguous, in frequency, resourceblocks; and the number of resource blocks in each resource window may beconfigured semi-statically. Each resource window has a same number ofsilent REs, and are configured semi-statically.

The present invention pertains to a method in a receiving unit 100 or atransmitting unit 110 of a wireless network, for facilitating noise andinterference measurements on an air interface. The method comprises thesteps of obtaining information relating to a time-varying layout of asilent resource element (RE) grid. There is the step of taking apresence of a silent RE grid into account in the reception of a controlor a data channel.

The step of obtaining information can include the steps of using apseudo-random sequence to generate said layout of said silent RE grid,and synchronizing the pseudo-random sequence by deriving a seed for thepseudo-random sequence from parameters known to both a receiving unit100 and a transmitting unit 110. The pseudo-random sequence can besynchronized in each frame based on the parameters that includes a cellID and a frame index. The layout of the silent RE grid can be receivedthrough signaling.

There can be the steps of collecting statistics relating to inter-cellinterference based on measurements on the silent RE grid in anelectronic memory 16 having codes using the statistics with the code toestimate any or all of: a channel quality indicator, inter-cell powerthat hits a channel, a co-variance matrix of the inter-cell interferencethat hits the channel, a full probability distribution of the Inter-cellinterference; and sending the signal. There can be the step ofrandomizing the silent RE grid in consecutive, in frequency and time,resource blocks (RBs). There can be the step of deriving the silent REgrid with essentially no signaling overhead.

There can be the step of introducing another silent RE grid on a controlchannel to estimate the interference that hits the control channel usingcode in an electronic memory 16. There can be the step of coordinatingeach silent grid of neighboring cells in said wireless system such thatthere is no significant overlap. For each subframe, there can be thestep of grouping resource blocks into resource windows where eachresource window is a group of contiguous, in frequency, resource blocks;and the number of resource blocks in each resource window may beconfigured semi-statically. Each resource window has a same number ofsilent REs, and are configured semi-statically.

In more detail, the invention contains the following general steps, andexample realizations. In the following we focus on the data channel, butthe same approach, with straightforward modifications, can be applied toestimate the interference that hit the control channel.

Designing the Silent Grids

Several aspects should be kept in mind when designing the silent grid.

The interference on the silent grid should reflect the interferencestatistics of the data channel as a whole. Therefore distribution ofsilent REs over the data channel should preferably be as uniform aspossible.

According to one embodiment the grid could be pseudo-random in the sensethat it should change over time and/or frequency to avoid significantlong-term overlap with silent grids of neighbouring cells.

It should be noted that the invention is not limited to pseudo-randomgrids; for example, an alternative method is to coordinate the silentgrid of neighbouring cells such that no significant overlap occur andthen signal the selected silent RE grid to the UEs dynamically orsemi-statically. Such an approach could however possibly require carefulplanning.

According to further embodiment the UEs should be able to readily derivewhich silent grid is being used, with little or preferably no controlsignalling overhead.

Alternatively it is conceivable to use explicit signalling of the silentgrid layout.

According to a further embodiment clustering of the silent REs in one ora few R s should be avoided for improved sample statistics.

A simple scheme, according to one embodiment, that achieves some or allof the criteria mentioned above is as follows:

-   -   For each subframe, the RBs are grouped into resource windows        (RW);    -   Each RW is a group of contiguous (in frequency) RBs;    -   The number of RBs in each RWV is configured semi-statically;    -   As special cases, there could be only one RW that represent the        entire system bandwidth, or there could be a RW for each RB.    -   For each RW, all REs that are not control or RS signalling are        enumerated;    -   In each RW, a specified number of silent REs are selected from        the set of enumerated REs using a pseudo-random number generator        that generates numbers uniformly in the range of the enumerated        data REs. Alternatively, selection of the silent RE are        coordinated. The grouping into RWs, will ensure that clustering        of silent REs is sufficiently limited. The number of selected        silent REs could be fixed, derived from the number of RBs in        each RW, or possible semi-statically configured.

The scheme can also readily be generalized to let a RW constitute only apart of a RB in the time domain; for example, the OFDM symbols in the RBcan be grouped so that symbols including RS symbols, and data symbols,are mapped to RW_RS and OFDM symbols carrying only data are mapped toRW_d. It is also conceivable to use a different number of silent REs inRW_RS and RW_d. Such a separation of the OFDM symbols can be usefulsince the inter-cell interference that hit RW_RS and RW_d will havedifferent statistics.

According to a further embodiment the power that is saved by remainingsilent on some REs can be redistributed to boost the power on other REsthat carry data or reference symbols. Such power reallocation combinedby the preceding method of assigning different OFDM symbols to differentRW categories, can be a useful approach to reallocated the power withinOFOM symbols, for example in order to support different powers on the REcarrying RS and the REs carrying data in the same OFDM symbol.

Determining and Configuring the Silent RE Grid

As indicated in the preceding, it is beneficial to let the silent REgrid be generated pseudo-randomly to transparently avoid consistentgrid-overlap with neighbouring cells. It is therefore necessary tosynchronize the random generators used at the NodeB with those in theUEs.

According to a further embodiment of the present invention a simplescheme for synchronizing the pseudo-random generators is to reinitializethe pseudo-random generators in each frame using a seed that is derivedfrom

1. Cell ID, to provide uniqueness for each cell.

2. Frame index, to provide hopping over time.

Both the cell ID and the frame index are available at the UEs. Note thatany re-initialization interval of the number generator can be used, aslong as there is a suitable index, available at the UE, that can be usedto progress the seed over time; this includes, but is not limited to, asubframe, or groups of frames.

If more flexibility is desired, such as configurable silent RE griddensities, some grid parameters could be set semi-statically usinghigher layer control signalling.

Measuring the Interference

The silent RE grid is used by the UEs to collect statistics of theinter-cell interference that hit the data channel. If the silent grid isuniformly distributed over the data channel, as suggested in thepreceding, the interference samples collected in the silent grid will,over time, be the same as the interference that hit the data channel asa whole. These samples can thus be utilized by the UE to estimate.

-   -   The inter-cell interference power that hits the data channel.    -   The co-variance matrix of the inter-cell interference that hits        the data channel. This is particularly useful if the UE has        multiple antennas    -   The full probability distribution of the inter-cell        interference.    -   The measured statistics can be average over time and frequency;        similar to the approach proposed in R1-074855, CQI Measurement        Methodology, Ericsson, 3GPP RAN1#51, Korea.

According to one embodiment the interference measurement on the silentRE grid can, for example, be used as a basis for the CQI reporting if itis combined with measurements of the received power of the data signals.Such a signal power estimate can, for instance, be obtained frommeasurements on the RS, taking potential signalling-power normalizationseffects into account.

Exemplary improvements of different aspects and embodiments of thepresent invention is improved capacity, coverage and quality, enabledthrough more accurate link adaptation, power control and scheduling, inturn enabled by more accurate interference estimation.

Moreover, the invention allows for inter-cell interference measurementsdirectly on the data channel with small computational-complexity. Thescheme also transparently manages inter-cell interference measurementsin multiuser-MIMO allocation scenarios.

Although the invention has been described in detail in the foregoingembodiments for the purpose of illustration, it is to be understood thatsuch detail is solely for that purpose and that variations can be madetherein by those skilled in the art without departing from the spiritand scope of the invention except as it may be described by thefollowing claims.

1. A method in a receiving unit of a wireless network, for facilitatingnoise and interference measurements on an air interface, said methodcomprising the steps of: obtaining information relating to atime-varying layout of a silent resource element (RE) grid; and taking apresence of a silent RE grid into account in the reception of a controlor a data channel.
 2. The method according to claim 1, wherein said stepof obtaining information comprises the steps of using a pseudo-randomsequence to generate said layout of said silent RE grid, andsynchronizing said pseudo-random sequence by deriving a seed for saidpseudo-random sequence from parameters. 3 The method according to claim2, wherein said pseudo-random sequence is synchronized in each framebased on said parameters that include a cell ID and a frame index. 4.The method according to claim 1, wherein said layout of said silent REgrid is received through signaling.
 5. The method according to claim 1including the steps of: collecting statistics relating to inter-cellinterference based on mesurements on said silent RE grid in anelectronic memory having code; using said statistics with the code toestimate any or all of: a channel quality indicator, inter-cell powerthat hits a channel, a co-variance matrix of the inter-cell interferencethat hits the channel, a full probability distribution of the Inter-cellinterference.
 6. The method according to claim 1 including the step ofrandomizing the silent RE grid in consecutive, in frequency and time,resource blocks (RBs).
 7. The method according to claim 1 including thestep of deriving the silent RE grid with essentially no signalingoverhead.
 8. A method according to claim 1 including the step ofintroducing another silent RE grid on a control channel to estimate theinterference that hits the control channel using code in an electronicmemory.
 9. The method as described in claim 1 including the step ofcoordinating each silent grid of neighboring cells in said wirelesssystem such that there is no significant overlap.
 10. The method asdescribed in claim 1 wherein for each subframe, grouping resource blocksinto resource windows where each resource window is a group ofcontiguous, in frequency, resource blocks; and the number of resourceblocks in each resource window may be configured semi-statically, eachresource window having a same number of silent REs, and are configuredsemi-statically.
 11. A method in a transmitting unit of a wirelessnetwork, for facilitating noise and interference measurements on an airinterface, said method comprising the steps of: obtaining informationrelating to a time-varying layout of a silent resource element (RE)grid; and taking a presence of a silent RE grid into account in thereception of a control or a data channel.
 12. A receiving unit of awireless network, for facilitating noise and interference measurementson an air interface comprising, a network interface which obtainsinformation relating to a time-varying layout of a silent resourceelement (RE) grid; an electronic memory having code in communicationwith the network interface which stores the information; and aprocessing unit in communication with the electronic memory that takes apresence of a silent RE grid into account in the reception of a controlor a data channel,
 13. The receiving unit as described in claim 12wherein the processing unit uses a pseudo-random sequence to generatethe layout of the silent RE grid, and synchronizes the pseudo-randomsequence by deriving a seed for the pseudo-random sequence fromparameters.
 14. The receiving unit as described in claim 13 wherein thepseudo-random sequence is synchronized in each frame by the processingunit based on parameters that include a cell ID and a frame index andthe layout of the silent RE grid is received through signaling by thenetwork interface.
 15. The receiving unit as described in claim 14wherein the electronic memory collects statistics relating to inter-cellinterference based on measurements on the silent RE grid.
 16. Thereceiving unit as described in claim 15 wherein the processing unit usesthe statistics with the code to estimate any or all of, a channelquality indicators inter-cell power that hits a channel, a co-variancematrix of the inter-cell interference that hits the channel, a fullprobability distribution of the Inter-cell interference; and sends thesignal through the network interface.
 17. The receiving unit asdescribed in claim 16 wherein the processing unit randomizes the silentRE grid in consecutive, in frequency and time, resource blocks (RBs).18. The receiving unit as described in claim 17 wherein the processingunit derives the silent RE grid with essentially no signaling overhead.19. The receiving unit as described in claim 18 wherein the processingunit introduces another silent RE grid on a control channel to estimatethe interference that hits the control channel using the code in theelectronic memory,
 20. The receiving unit as described in claim whereinthe processing unit coordinates each silent grid of neighboring cells inthe wireless system such that there is no significant overlap.
 21. Thereceiving unit as described in claim 20 wherein for each subframe, theprocessing unit groups resource blocks into resource windows where eachresource window is a group of contiguous, in frequency, resource blocks;and the number of resource blocks in each resource window may beconfigured semi-statically, and each resource window has a same numberof silent REs, and are configured semi-statically.
 22. A transmittingunit of a wireless network, for facilitating noise and interferencemeasurements on an air interface comprising: a network interface whichobtains information relating to a time-varying layout of a silentresource element (RE) grid; an electronic memory having code incommunication with the network interface which stores the information,and a processing unit in communication with the electronic memory thattakes a presence of a silent RE grid into account in the transmission ofa control or a data channel.